Apparatus and methods for reducing soft buffer size in MTC devices

ABSTRACT

A machine type communication (MTC) device is configured to communicate through a long term evolution (LTE) network. The MTC device include a wireless transceiver to receive a signal through the LTE network, a soft buffer configured to store a plurality of soft channel bits for up to a maximum number of hybrid automatic retransmission request (HARQ) processes, and a signal processing unit. The signal processing unit is configured to determine a total number of soft channel bits based at least on the maximum number of HARQ processes, and to use limited buffer rate matching (LBRM) to store a reduced number of the total number of soft channel bits in the soft buffer.

RELATED APPLICATIONS

This application claims the benefit under 35 U.S.C. §119(e) of U.S.Provisional Application No. 61/968,282, filed Mar. 20, 2014, U.S.Provisional Application No. 61/985,391, filed Apr. 28, 2014, and U.S.Provisional Application No. 61/990,619, filed May 8, 2014, each of whichis hereby incorporated by reference herein in its entirety.

TECHNICAL FIELD

This disclosure relates generally to wireless communication networks.Specifically, this disclosure relates to low-cost machine typecommunication (MTC) devices.

BACKGROUND INFORMATION

Machine type communication (MTC), also called machine to machine (M2M)communication, is of interest to mobile network operators, equipmentvendors, MTC specialist companies, and research bodies. M2Mcommunications enable M2M components to be interconnected, networked,and controlled remotely with low-cost scalable and reliabletechnologies. Such M2M communications could be carried over mobilenetworks, in which case the role of mobile network is largely confinedto serve as a transport network.

A user equipment device (or simply, UE) used as an MTC device for MTCcommunications in MTC applications (or simply, MTC) has characteristicssuch as being nomadically (re-)deployed, having low mobility whiledeployed, being deployed in locations with low signal strength (e.g., in“poor coverage areas”), proving low priority communications, andinfrequently sending small amounts of mobile originated (MO) or mobileterminated (MT) data. For example, a smart meter for utility meteringapplications is a type of UE used as an MTC device (referred togenerally as a UE). Such metering devices could monitor municipalutility service usage to periodically report information on energyconsumption to service providers. Metering devices may autonomously pushreports of usage information to a centralized node in a network, or thecentralized node may poll metering devices as reporting information isneeded.

Road security is another example application of monitoring. Forinstance, in the event of a car accident, an in-vehicle emergency callservice would autonomously report location information of the caraccident to an emergency first responder and thereby facilitate promptassistance. Other road-security applications for monitoring includeintelligent traffic management, automatic ticketing, fleet management,and other uses.

Consumer electronics, including devices such as eBook readers, digitalcameras, personal computers, and navigation systems, could also benefitfrom monitoring. For example, such devices could use monitoring toupgrade firmware or to upload and download online content.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a communication network according tocertain embodiments.

FIG. 2 is a block diagram of an example MTC device according to oneembodiment.

FIG. 3 is a block diagram of the signal processing unit shown in FIG. 2according to one embodiment.

FIG. 4 illustrates an example embodiment of limited buffer rate matching(LBRM).

FIGS. 5A, 5B, 6A, 6B, 7A, and 7B are graphs showing performancecomparisons between full buffer rate matching (FBRM) and LBRM accordingto certain embodiments.

FIGS. 8A, 8B, 9A, and 9B illustrate example hybrid automaticretransmission request (HARQ) processes for a low-cost MTC deviceaccording to certain embodiments.

FIG. 10 is an example illustration of a mobile device according to oneembodiment.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

A detailed description of systems and methods consistent withembodiments of the present disclosure is provided below. While severalembodiments are described, it should be understood that disclosure isnot limited to any one embodiment, but instead encompasses numerousalternatives, modifications, and equivalents. In addition, whilenumerous specific details are set forth in the following description inorder to provide a thorough understanding of the embodiments disclosedherein, some embodiments can be practiced without some or all of thesedetails. Moreover, for the purpose of clarity, certain technicalmaterial that is known in the related art has not been described indetail in order to avoid unnecessarily obscuring the disclosure.

MTC devices are generally low-cost devices. However, there is an effortto further reduce the cost and size of low-cost MTC devices. Asdiscussed below, rate matching in user equipment (UE), such as MTCdevices, generally uses a large amount of memory to store soft channelbits for hybrid automatic retransmission request (HARQ) processes. Thesoft channel bits are related to the implementation of soft buffer size.Certain embodiments disclosed herein reduce the soft channel bits toreduce size and cost in terms of memory for MTC devices. In suchembodiments, the soft buffer size is a function of a maximum supportedtransport block (TB) size, the number of HARQ processes, turbo encodingand decoding, and application of limited buffer rate matching (LBRM).Certain embodiments may reduce the number of soft channel bits by about50%, as compared to other approaches using the same number of HARQprocesses. In addition, or in other embodiments, the cost savings may beincreased by lowering the number of HARQ processes for low-cost MTCdevices.

In a third generation partnership project (3GPP) radio access network(RAN) long term evolution (LTE) system, a node may be a combination ofEvolved Universal Terrestrial Radio Access Network (E-UTRAN) Node Bs(also commonly denoted as evolved Node Bs, enhanced Node Bs, eNodeBs, oreNBs) and Radio Network Controllers (RNCs), which communicate with awireless device, known as a user equipment (UE). The DL transmission maybe a communication from the node (e.g., eNB) to the wireless device(e.g., UE), and the UL transmission may be a communication from thewireless device to the node. As used herein, the terms “node” and “cell”are both intended to be synonymous and refer to a wireless transmissionpoint operable to communicate with multiple user equipment, such as aneNB, a low power node, or other base station.

FIG. 1 is a block diagram of a communication network 100 including anode (eNB 110) configured to communicate uplink (UL) and downlink (DL)user data 112 with a UE (low-cost MTC device 114) according to certainembodiments. The MTC device 114 is shown within a coverage area 116 ofthe eNB 110. The MTC device 114 may also be configured for directcommunication 118 with another UE 120. While the example shows the UE120 within the coverage area 116 of the eNB 110, the directcommunication 118 may also occur when the UE 120 is located outside thecoverage area 116. The MTC device 114 is configured in certainembodiments to use LBRM to reduce the number of soft channel bits forHARQ processes.

FIG. 2 is a block diagram of an example MTC device 114 according to oneembodiment. Embodiments described herein relate to the MTC device 114operable in a wireless communication system, such as the communicationnetwork 100 shown in FIG. 1. The MTC device 114 is configured to useLBRM to reduce the number of soft channel bits for HARQ processes.

The MTC device 114 includes an arrangement 208, which is shownsurrounded by a dashed line. The MTC device 114 may be a low-cost MTCdevice. The MTC device 114 and arrangement 208 is further illustrated asto communicate with other entities via a communication unit 210, whichmay be regarded as part of the arrangement 208. The communication unit210 comprises means for communication, such as a receiver (Rx) 222 and atransmitter (Tx) 220, or a transceiver. The communication unit 210 mayalternatively be denoted “interface”. The arrangement may furthercomprise other functional units 217, such as functional units providingregular UE functions, and may further comprise one or more memory units216.

The arrangement 208 may be implemented, for example, by one or more of:a processor or a microprocessor and adequate software and memory forstoring thereof, a programmable logic device (PLD) or other electroniccomponent(s) or processing circuitry configured to perform the actionsdescribed herein.

The arrangement 208 comprises a receiver unit 212, adapted to receive asignal via a carrier (e.g., an UL carrier, a DL carrier, an M2M carrier,or a device to device (D2D) carrier). The receiver unit 212 passes thesignal to a signal processing unit 214.

FIG. 3 is a block diagram of the signal processing unit 214 shown inFIG. 2 according to one embodiment. The signal processing unit 214 maybe implemented in hardware, software, or a combination of the two. Thesignal processing unit 214 is organized into functional blocks depictedin FIG. 3. The signal is received by the transceiver in FIG. 2, whichdemodulates the signal and generates received log-likelihood ratios(LLRs) for a given TB. A HARQ combining element 310 combines thereceived LLRs with stored LLRs for the TB from a previous transmission.The combined LLRs are decoded by the processor 304 at block 312 (e.g., aturbo decoder) and may be passed to another process (e.g., sent tohigher layers for further processing). If the TB is not successfullydecoded (as determined, e.g., by a cyclic redundancy check (CRC)function of the signal processing unit 214), then the combined LLRs forthat TB are stored in a partition 316 of a soft buffer 314. If a TB isnot successfully decoded at block 312, the MTC device 114 may transmitthe HARQ feedback on its uplink. The soft buffer 314 holds the combinedLLR for a TB until the MTC device 114 makes another attempt to decodethe TB.

The transmitting entity (e.g., the eNB 110 or the UE 120 shown in FIG.1), upon receiving the HARQ feedback indicating the MTC device 114 hasnot successfully received the TB, attempts to retransmit the TB. Theretransmitted TB is put through the same functional blocks as before,but when the MTC device 114 attempts to decode the retransmitted TB atblock 312, the MTC device 114 retrieves the LLRs for the TB from itsmemory unit 216, and uses the HARQ combining element 310 to combine thereceived LLRs and the stored LLRs for the TB in a process known as “softcombining.” The combined LLRs are provided to the decoder at block 312,which decodes the TB and provides the successfully decoded TB to higherlayers for further processing.

The soft buffer 314 may also be referred to as a HARQ memory or HARQbuffer. Since there are multiple HARQ processes, a HARQ process index orHARQ identity (typically signaled using an explicit field withindownlink control information (DCI) format associated with the TB (e.g.for downlink), or implicitly determined via subframe number (SN), systemframe number (SFN), etc. (e.g. for uplink)) is made available for theHARQ combining element 310 to correctly perform the combining operation.For the uplink transmission, the implicit HARQ process index is used bythe MTC device 114 to correctly determine the coded bits for uplinktransmissions. If the MTC device 114 is configured with a transmissionmode with a maximum of one TB per HARQ process (or one TB pertransmission timing interval (TTI)), the soft buffer 314 of the MTCdevice 114 may be divided into eight partitions 316, as shown in FIG. 3.

For frequency division duplexing (FDD), for a given component carrier,the MTC device 114 may have eight HARQ processes in DL. In somescenarios, if the MTC device 114 has insufficient amount of storage fora given transport block, and a decoding failure occurs, the MTC device114 may choose to store some LLRs and discard some other LLRs. In otherscenarios, if no storage is available or no storage is deemed necessaryfor a transport block, if a decoding failure occurs, the MTC device 114may discard all LLRs corresponding to the transport block. Suchscenarios typically occur where the network entity transmits a quantityof coded bits that exceed the storage capacity of the UE. For FDD, andfor uplink, for a given component carrier, the MTC device 114 may haveeight HARQ processes when the MTC device 114 is not configured inUL-MIMO transmission mode. For TDD, the number of HARQ processes for theuplink is determined based on the TDD UL/DL configuration.

With reference to Table 1, the soft buffer dimensioning for a low-costMTC device (i.e., a UE Category 0 in 3GPP LTE standards) when using fullbuffer rate matching (FBRM) is determined by the total number of softchannel bits. The derivation of the soft buffer size is based on themaximum TB size, turbo encoding/decoding, and the number of HARQprocesses.

TABLE 1 DL physical layer parameter values set by field ue-CategoryMaximum Maximum Maximum number of number of DL- number of bits Totalsupported SCH transport a DL-SCH number layers for block bits transportblock of soft spatial received within received within channelmultiplexing in UE Category a TTI a TTI bits DL Category 0 1000 100025344 1

For low cost MTC devices using FBRM, the soft buffer size corresponds tothe total number of soft channel bits (25344 bits), which is derived asfollows:

-   -   Maximum TB per TTI: 1000 bits;    -   TB size per codeword (B): 1000;    -   Number of codeblocks (C): Ceil{(B=24/(6144−24}=1;    -   TB size together with cyclic redundancy check (CRC), (B′):        (B+24)=1024;    -   Turbo code interleave size (K): B′/C=1024;    -   Turbo code trellis term (T): K+4=1028;    -   Subblock interleave size (V)=Ceil(T/32)32=1056;    -   Number of padding bits: V−T=28;    -   Total soft buffer size: V*(1/mother coding rate)*C*(max HARQ        processes)=1056*3*1*8=25344 bits, where the mother coding rate=⅓        and max HARQ processes=8.

Certain embodiments further reduce the cost of low-cost MTC devices byapplying LBRM to reduce the total number of soft channel bits. For LTE,up to 50% soft buffer reduction is provided by LBRM for the higher UEcategories (e.g., 3, 4, and 5), while it is not applied to the lower UEcategories (e.g., 1 and 2). There may be little or no noticeableperformance difference, particularly when up to four HARQ processes areused. Even when using more than four HARQ processes, the performancedegradation using LBRM may be very marginal.

FIG. 4 illustrates an example embodiment of LBRM. After turbo encoding,the encoded bit size becomes three times (3×) the information bit size.Thus, in the example shown in FIG. 4, 32 sub-block interleave columnscorrespond to the information bits and would be repeated three times(32×3=96 columns) for FBRM. For LBRM, however, the soft buffer size isreduced by forcing an early wrap-around after N columns. LBRM alsocompresses the redundancy version (RV) locations (shown as RV0, RV1,RV2, and RV3) so that each of the RVs is located prior to thewrap-around point. RV is defined by four equal divisions of the numberof sub-block interleave columns after LBRM (N/4). The RV0 is offset bytwo columns and an RV definition column is quantized by two columns.

As shown in Table 2, in certain embodiments, using LBRM with low-costMTC devices reduces the soft buffer size to 12672 (=25344/2) bits. Ingeneral, the total number of soft channel bits is calculated with LBRMas follows:Total number of soft channel bits=V*(mother code rating)*C*(max HARQprocesses)/2.Note that if any parameters to derive V (subblock interleave size) arechanged, it may be reflected by the above equation (as illustrated inexamples below).

TABLE 2 DL physical layer parameter values set by field ue-Category withLBRM Maximum Maximum Maximum number of number of DL- number of bitsTotal supported SCH transport a DL-SCH number layers for block bitstransport block of soft spatial received within received within channelmultiplexing in UE Category a TTI a TTI bits DL Category 0 1000 100012672 1

For low-cost MTC devices, there is little or no performance loss betweenLBRM and FBRM when TB size (TBS) is equal to or smaller than(TBS_max/2), or when the MTC device is operating around thesignal-to-noise ratio (SNR) point, or when effective coding rate isequal to or greater than (2*TBS)/(3*TBS_max) with CC (Chase Combining)or for initial transmission only with incremental redundancy (IR).

For example, FIGS. 5A, 5B, 6A, 6B, 7A, and 7B are graphs showingperformance comparisons between FBRM and LBRM according to certainembodiments. The illustrated performance comparisons between FBRM andLBRM are in terms of initial transmission block error rate (BLER) inFIGS. 5A, 6A, and 7A, and normalized throughput in FIGS. 5B, 6B, and 7B.FIGS. 5A and 5B illustrate examples using quadrature phase shift keying(QPSK) and six physical resource blocks (PRBs). FIGS. 6A and 6Billustrate examples using 16-quadrature amplitude modulation (QAM) andthree PRBs. FIGS. 7A and 7B illustrate examples using 64 QAM and twoPRBs. The simulation model and parameters for each of the example graphsinclude a bandwidth of 10 MHz, a carrier frequency of 2 GHz, an FDDframe type, a TM2 transmission mode, a multiple input multiple output(MIMO) configuration of 2×1 with low correlation, an extended pedestrianA (EPA) channel model, a Doppler shift of 1 Hz, and a target BLER of10%. In the simulations, two TBS sizes are considered: 500 and 1000bits, which correspond to effective coding rates of ⅓ and ⅔,respectively.

From the plots, it can be observed that BLER performance difference forinitial transmission between FBRM and LRBM is negligible. In addition,when considering the operating SNR points (assuming 10% BLER in FIGS.5A, 6A and 7A), no throughput performance degradation is observed forLBRM. Accordingly, in certain embodiments, a low-cost MTC device usesLBRM and includes a soft buffer size of no more than 12672 bits.

In addition, or in other embodiments, the soft buffer size is reducedeven more when half-duplex FDD (HD-FDD) is used to reduce the number ofHARQ processes. For HD-FDD, due to half-duplex restraints (e.g.,simultaneous transmit and receive may not be allowed), in certainembodiments, not every subframe (SF) can be used for transmitting andreceiving. Thus, the number of HARQ processes can be reduced to furtherreduce the soft buffer size.

For example, FIGS. 8A, 8B, 9A, and 9B illustrate example HARQ processesfor a low-cost MTC UE according to certain embodiments. In theseexamples, a transition time between UL and DL may be up to about 1 ms(one subframe) e.g., if a single oscillator is used for the low-cost MTCUE.

FIG. 8A shows a HARQ procedure for half duplex in a low-cost MTC UE witha 1 ms transition time. HARQ-ACKs corresponding to physical downlinkshared channels (PDSCHs) at SF0 and SF1 are transmitted from a node to aUE at SF4 and SF5, respectively. If the PDSCHs are successfully decodedat the MTC UE (i.e., the MTC UE sends ACK to eNB), a new PDSCH can betransmitted in the next available subframe SF7 and SF8. SF2 and SF6 areused for transition time for DL to UL and for UL to DL, respectively.

A first HARQ process corresponds to SF0 and SF8 (as denoted by “0” aboveSF0 and SF8). A second HARQ process corresponds to SF1 (as denoted by“1” above SF1). A third HARQ process is corresponding to SF7 (as denotedby “2”) above SF7). In this example, SF2, SF3, SF4, SF5, and SF6 cannotbe used by the MTC UE for reception (DL) for HD-FDD due to switchingtime and UL transmission. Further, the MTC UE cannot use SF0, SF1, SF2,SF3, SF6, SF7, and SF8 for transmission (UL) for HD-FDD due to switchingtime and DL reception. From the illustrated operation, the maximumnumber of HARQ processes for half duplex low cost MTC UE is three. Asshown in Table 3, when the number of HARQ processes for HD-FDD is three,the total number of soft channel bits with LBRM can be 1056*3*1*3/2=4752bits.

While the example shown in FIG. 8A shows SF7 used for a third HARQprocess, FIG. 8B shows an example where SF7 is not used for a HARQprocess. Accordingly, the maximum number of HARQ processes is two forthe half duplex in low cost MTC UE with 1 ms transition time in FIG. 8B.As shown in Table 3, when the number of HARQ processes for HD-FDD istwo, the total number of soft channel bits with LBRM may be1056*3*1*2/2=3168 bits.

If considering the HARQ buffer for system information block (SIB)-1together, the maximum number of HARQ processes for half duplex low costMTC UE is four, which Table 3 shows corresponds to 4752 total softchannel bits for HD-FDD. The maximum number of HARQ processes for halfduplex low cost MTC UE can also be one to have a minimum cost. As shownin Table 3, when the number of HARQ processes for HD-FDD is 1, the totalnumber of soft channel bits with LBRM can be 1056*3*1*1/2=1584 bits.

TABLE 3 Total number of soft channel bits according to number of HARQprocesses for HD-FDD HD-FDD with LBRM HD-FDD with FBRM Total Costsavings Total Cost savings Number of number of (%) compared to number(%) compared to HARQ soft conventional of soft conventional processesfor channel 25344 total soft channel 25344 total soft HD-FDD bitschannel bits bits channel bits 1 1584 93.75 3168 87.5 2 3168 87.5 633675 3 4752 81.25 9504 62.5 4 6336 75 12672 50 5 7920 68.75 15840 37.5 69504 62.5 19008 25 7 11088 56.25 22174 12.5 8 12672 50 25344 0

At least some of the values shown in Table 3 may also apply tofull-duplex FDD (FD-FDD). Further, the values shown in Table 3 areprovided by way of example and persons skilled in the art will recognizefrom the disclosure herein that changes to system configurations mayproduce different results for the total number of soft channel bits. Forexample, Table 4 shows variations in certain system parameters when themaximum TBS=968 bits and when the maximum TBS=1032 bits. Table 5 andTable 6 show the resulting changes to the total number of soft channelbits.

TABLE 4 Example parameters with max TBS of 968 bits and 1032 bits MaxTBS = 968 bits Max TBS = 1032 bits TB size per codeword (B) 968 1032Number of codeblocks (C) 1 1 TB size together with CRC 992 1056 (B′)Turbo code interleave size 992 1056 (K) Turbo code trellis term (T) 9961060 Subblock interleave size 1024 1088 (V) Total soft buffer size 2457626112

TABLE 5 Total number of soft channel bits for max TBS of 968 bits HD-FDDwith LBRM HD-FDD with FBRM Total Cost savings Total Cost savings Numberof number (%) compared to number of (%) compared to HARQ of softconventional soft conventional processes for channel 25344 total softchannel 25344 total soft HD-FDD bits channel bits bits bits 1 1536 93.753072 87.5 2 3072 87.5 6144 75 3 4608 81.25 9216 62.5 4 6144 75 12288 505 7680 68.75 15360 37.5 6 9216 62.5 18432 25 7 10752 56.25 21504 12.5 812288 50 24576 0

TABLE 6 Total number of soft channel bits for max TBS of 1032 bitsHD-FDD with LBRM HD-FDD with FBRM Total Cost savings Total Cost savingsNumber of number (%) compared to number of (%) compared to HARQ of softconventional soft conventional processes for channel 25344 total softchannel 25344 total soft HD-FDD bits channel bits bits channel bits 11632 93.75 3264 87.5 2 3264 87.5 6528 75 3 4896 81.25 9792 62.5 4 652875 13056 50 5 8160 68.75 16320 37.5 6 9792 62.5 19584 25 7 11424 56.2522848 12.5 8 13056 50 26112 0

Other parameters may be changed to reduce the number of HARQ processes.For example, FIGS. 9A and 9B illustrate example HARQ processes for alow-cost MTC UE with different HARQ round trip timer (RTT) timers. TheHARQ RTT timer is a parameter that specifies a minimum amount ofsubframe(s) before DL HARQ retransmission is expected by the UE. FIG. 9Ashows the HARQ operation with 1 ms transmission gap for HARQ RTTtimer=14. By changing HARQ RTT timer from 8to 14, the maximum number ofHARQ processes becomes four. Similarly, FIG. 9B shows the HARQ operationwith 1 ms transition gap for HARQ RTT timer =7. By changing HARQ RTTtimer from 8 to 7, the maximum number of HARQ processes becomes two.

There may be a trade-off between the number of HARQ processes and theHARQ RTT timer. With a larger HARQ RTT timer, a larger maximum number ofHARQ processes can be achieved. For example, if the HARQ RTT timer=21,the maximum number of HARQ processes becomes six.

Table 7 shows further examples of different HARQ RTT timers andcorresponding maximum number of HARQ processes. According to certainembodiments, the relationship between the HARQ RTT timer and maximumnumber of HARQ processes are given by 2*(HARQ RTT Timer)/7”.

TABLE 7 Max number of HARQ processes according to HARQ RTT timer HARQRTT timer Maximum number of HARQ processes 7 2 14 4 21 6 28 8 35 10

FIG. 10 is an example illustration of a mobile device, such as a UE, amobile station (MS), a mobile wireless device, a mobile communicationdevice, a tablet, a handset, or another type of wireless communicationdevice. The mobile device can include one or more antennas configured tocommunicate with a transmission station, such as a base station (BS), aneNB, a base band unit (BBU), a remote radio head (RRH), a remote radioequipment (RRE), a relay station (RS), a radio equipment (RE), oranother type of wireless wide area network (WWAN) access point. Themobile device can be configured to communicate using at least onewireless communication standard, including 3GPP LTE, WiMAX, high speedpacket access (HSPA), Bluetooth, and Wi-Fi. The mobile device cancommunicate using separate antennas for each wireless communicationstandard or shared antennas for multiple wireless communicationstandards. The mobile device can communicate in a wireless local areanetwork (WLAN), a wireless personal area network (WPAN), and/or a WWAN.

FIG. 10 also provides an illustration of a microphone and one or morespeakers that can be used for audio input and output from the mobiledevice. The display screen may be a liquid crystal display (LCD) screenor other type of display screen, such as an organic light emitting diode(OLED) display. The display screen can be configured as a touch screen.The touch screen may use capacitive, resistive, or another type of touchscreen technology. An application processor and a graphics processor canbe coupled to internal memory to provide processing and displaycapabilities. A non-volatile memory port can also be used to providedata input/output options to a user. The non-volatile memory port mayalso be used to expand the memory capabilities of the mobile device. Akeyboard may be integrated with the mobile device or wirelesslyconnected to the mobile device to provide additional user input. Avirtual keyboard may also be provided using the touch screen.

Additional Example Embodiments

The following are examples of further embodiments:

Example 1 is a MTC device configured to communicate through a LTEnetwork that includes a wireless transceiver, a soft buffer, and asignal processing unit. The wireless transceiver is configured toreceive a signal through the LTE network. The soft buffer is configuredto store a plurality of soft channel bits for up to a maximum number ofHARQ processes. The signal processing unit is configured to determine atotal number of soft channel bits based on the maximum number of HARQprocesses, a subblock interleave size, a coding rate, and a number ofcode blocks and to store, with LBRM, a reduced number of the totalnumber of soft channel bits in the soft buffer.

In Example 2, the reduced number of Example 1 includes half of the totalnumber of soft channel bits.

In Example 3, the soft buffer of any of Examples 1-2 is sized to storeonly the reduced number of the total number of soft channel bits.

In Example 4, the MTC device of any of Examples 1-3 is defined in theLTE network within a UE category corresponding to 25344 total number ofsoft channel bits for downlink communication with an eNB, and whereinthe reduced number of the total number of soft channel bits includes12672 bits.

In Example 5, the maximum number of HARQ processes in any of Examples1-4 is eight.

In Example 6, the signal processor of any of Examples 1-5 determines thetotal number of soft channel bits based on a reduced maximum number ofHARQ processes for HD-FDD.

In Example 7, the reduced maximum number of HARQ processes of Example 6includes four HARQ processes, and the reduced number of the total numberof soft channel bits includes 6336 bits.

In Example 8, the reduced maximum number of HARQ processes of any ofExamples 6-7 includes three HARQ processes, and the reduced number ofthe total number of soft channel bits includes 4752 bits.

In Example 9, the signal processor of any of Examples 1-8 determines thetotal number of soft channel bits based on a reduced maximum number ofHARQ processes, and wherein the reduced maximum number of HARQ processesis based on a HARQ RTT timer.

Example 10 is a method that includes receiving a signal corresponding toa MTC device. The method includes demodulating the signal to generate aplurality of received LLRs corresponding to a transport block. Themethod include combining the received LLRs with a limited number ofstored LLRs for the transport block from a previous signal. The methodincludes decoding the combined LLRs and performing a cyclic redundancycheck to determine that the decoding failed. The method includes, inresponse to determining that the decoding failed, performing limitedbuffer rate matching to store only a limited number of the combined LLRsin a soft buffer, and requesting transmission of at least one additionalsignal corresponding to the transport block.

In Example 11, performing the limited buffer rate matching in Example 10includes storing half of the combined LLRs in the soft buffer.

In Example 12, the MTC device of any of Examples 10-11 includes a lowcost MTC device configured to communicate through a LTE network.

In Example 13, the low cost MTC device of Example 12 includes a category0 UE.

In Example 14, the requesting transmission of the at least oneadditional signal corresponding to the transport block of any ofExamples 10-13 is part of a HARQ process, and wherein the method furthercomprises reducing a maximum number of HARQ processes for the transportblock based on using HD-FDD communication with a network node.

In Example 15, the requesting transmission of the at least oneadditional signal corresponding to the transport block of any ofExamples 10-14 is part of a HARQ process, and wherein the method furthercomprises reducing a maximum number of HARQ processes for the transportblock based on a HARQ RTT timer value.

Example 16 is an apparatus that includes means to perform a method as inany of Examples 10-15.

Example 17 is a machine readable storage including machine-readableinstructions to implement a method or realize an apparatus as in any ofExamples 10-16.

Example 18 is an apparatus that includes processing logic configured toperform a method as in any of Examples 10-15.

Example 19 is a method for communicating through a LTE network. Themethod includes receiving a signal through the LTE network and storing aplurality of soft channel bits for up to a maximum number of HARQprocesses. The method includes determining a total number of softchannel bits based on the maximum number of HARQ processes, a subblockinterleave size, a coding rate, and a number of code blocks. The methodincludes storing, with LBRM, a reduced number of the total number ofsoft channel bits in the soft buffer.

Example 20 is an apparatus that includes means to perform a method as inExamples 19.

Example 21 is a machine readable storage including machine-readableinstructions to implement a method or realize an apparatus as in any ofExamples 19-20.

Example 22 is an apparatus that includes processing logic configured toperform a method as in Example 19.

Example 23 is a computer program product comprising a computer-readablestorage medium storing program code for causing one or more processorsto perform a method. The method includes establishing a connection withan evolved Node B (eNB) in a long term evolution (LTE) network;determining a maximum number of hybrid automatic retransmission request(HARQ) processes for full duplex frequency division duplexing with theeNB; determining a reduced number of HARQ processes for half duplexfrequency division duplexing with the eNB; the number being less thanthe maximum number; determining a total number of soft channel bitsbased on the reduced number of HARQ processes; and storing a reducednumber of the total number of soft channel bits in a soft buffer.

Example 24 includes the subject matter of Example 23, wherein storingthe reduced number of the total number of the soft channel bitscomprises performing limited buffer rate matching.

Example 25 includes the subject matter of any of Examples 23-24, whereinthe reduced number of the total number of the soft channel bitscomprises half of the total number of soft channel bits.

Example 26 includes the subject matter of any of Examples 23-25, whereinthe soft buffer is sized to store only the reduced number of the totalnumber of soft channel bits.

Example 27 includes the subject matter of any of Examples 23-26, whereinthe method further comprises configuring a user equipment (UE) as amachine type communication device for half duplex frequency divisionduplexing with the eNB.

Various techniques disclosed herein, or certain aspects or portionsthereof, may take the form of program code (i.e., instructions) embodiedin tangible media, such as floppy diskettes, CD-ROMs, hard drives, anon-transitory computer readable storage medium, or any othermachine-readable storage medium wherein, when the program code is loadedinto and executed by a machine, such as a computer, the machine becomesan apparatus for practicing the various techniques. In the case ofprogram code execution on programmable computers, the computing devicemay include a processor, a storage medium readable by the processor(including volatile and non-volatile memory and/or storage elements), atleast one input device, and at least one output device. The volatile andnon-volatile memory and/or storage elements may be a RAM, an EPROM, aflash drive, an optical drive, a magnetic hard drive, or another mediumfor storing electronic data. The eNB (or other base station) and UE (orother mobile station) may also include a transceiver component, acounter component, a processing component, and/or a clock component ortimer component. One or more programs that may implement or utilize thevarious techniques described herein may use an application programminginterface (API), reusable controls, and the like. Such programs may beimplemented in a high-level procedural or an object-oriented programminglanguage to communicate with a computer system. However, the program(s)may be implemented in assembly or machine language, if desired. In anycase, the language may be a compiled or interpreted language, andcombined with hardware implementations.

It should be understood that many of the functional units described inthis specification may be implemented as one or more modules orcomponents, which are terms used to more particularly emphasize theirimplementation independence. For example, a module or component may beimplemented as a hardware circuit comprising custom very large scaleintegration (VLSI) circuits or gate arrays, off-the-shelf semiconductorssuch as logic chips, transistors, or other discrete components. A moduleor component may also be implemented in programmable hardware devicessuch as field programmable gate arrays, programmable array logic,programmable logic devices, or the like.

Modules or components may also be implemented in software for executionby various types of processors. An identified component of executablecode may, for instance, comprise one or more physical or logical blocksof computer instructions, which may, for instance, be organized as anobject, a procedure, or a function. Nevertheless, the executables of anidentified module or component need not be physically located together,but may comprise disparate instructions stored in different locationsthat, when joined logically together, comprise the module or componentand achieve the stated purpose for the module or component.

Indeed, a module or component of executable code may be a singleinstruction, or many instructions, and may even be distributed overseveral different code segments, among different programs, and acrossseveral memory devices. Similarly, operational data may be identifiedand illustrated herein within modules or components, and may be embodiedin any suitable form and organized within any suitable type of datastructure. The operational data may be collected as a single data set,or may be distributed over different locations including over differentstorage devices, and may exist, at least partially, merely as electronicsignals on a system or network. The modules or components may be passiveor active, including agents operable to perform desired functions.

Reference throughout this specification to “an example” means that aparticular feature, structure, or characteristic described in connectionwith the example is included in at least one embodiment of the presentinvention. Thus, appearances of the phrase “in an example” in variousplaces throughout this specification are not necessarily all referringto the same embodiment.

As used herein, a plurality of items, structural elements, compositionalelements, and/or materials may be presented in a common list forconvenience. However, these lists should be construed as though eachmember of the list is individually identified as a separate and uniquemember. Thus, no individual member of such list should be construed as ade facto equivalent of any other member of the same list solely based onits presentation in a common group without indications to the contrary.In addition, various embodiments and examples of the present inventionmay be referred to herein along with alternatives for the variouscomponents thereof. It is understood that such embodiments, examples,and alternatives are not to be construed as de facto equivalents of oneanother, but are to be considered as separate and autonomousrepresentations of the present invention.

Although the foregoing has been described in some detail for purposes ofclarity, it will be apparent that certain changes and modifications maybe made without departing from the principles thereof. It should benoted that there are many alternative ways of implementing both theprocesses and apparatuses described herein. Accordingly, the presentembodiments are to be considered illustrative and not restrictive, andthe invention is not to be limited to the details given herein, but maybe modified within the scope and equivalents of the appended claims.

It will be understood by those having skill in the art that many changesmay be made to the details of the above-described embodiments withoutdeparting from the underlying principles of the invention. The scope ofthe present invention should, therefore, be determined only by thefollowing claims.

The invention claimed is:
 1. A machine type communication (MTC) deviceconfigured to communicate through a long term evolution (LTE) network,the MTC device comprising: a user equipment (UE) category 0 wirelesstransceiver to receive a signal through the LTE network; a soft bufferconfigured to store a plurality of soft channel bits for up to a maximumnumber of hybrid automatic retransmission request (HARQ) processes; anda signal processing unit to: determine a total number of soft channelbits based on the maximum number of HARQ processes, a subblockinterleave size, a coding rate, and a number of code blocks; and store,with limited buffer rate matching (LBRM), a reduced number of the totalnumber of soft channel bits in the soft buffer.
 2. The MTC device ofclaim 1, wherein the reduced number comprises half of the total numberof soft channel bits.
 3. The MTC device of claim 1, wherein the softbuffer is sized to store only the reduced number of the total number ofsoft channel bits.
 4. The MTC device of claim 1, wherein the MTC deviceis defined in the LTE network within a user equipment (UE) categorycorresponding to 25344 total number of soft channel bits for downlinkcommunication with an Evolved Universal Terrestrial Radio Access Network(E-UTRAN) Node B (eNB), and wherein the reduced number of the totalnumber of soft channel bits comprises 12672 bits.
 5. The MTC device ofclaim 4, wherein the maximum number of HARQ processes is eight.
 6. TheMTC device of claim 1, wherein for half-duplex frequency divisionduplexing (HD-FDD), the signal processor determines the total number ofsoft channel bits based on a reduced maximum number of HARQ processes.7. The MTC device of claim 6, wherein the reduced maximum number of HARQprocesses comprises four HARQ processes, and wherein the reduced numberof the total number of soft channel bits comprises 6336 bits.
 8. The MTCdevice of claim 6, wherein the reduced maximum number of HARQ processescomprises three HARQ processes, and wherein the reduced number of thetotal number of soft channel bits comprises 4752 bits.
 9. The MTC deviceof claim 1, wherein the signal processor determines the total number ofsoft channel bits based on a reduced maximum number of HARQ processes,and wherein the reduced maximum number of HARQ processes is based on aHARQ round trip timer (RTT).
 10. The MTC device of claim 1, furthercomprising at least one of an antenna, a touch sensitive display screen,a speaker, a microphone, a graphics processor, an application processor,internal memory, a non-volatile memory port, or combinations thereof.11. A machine type communication (MTC) device configured to communicatethrough a long term evolution (LTE) network, the MTC device comprising:a wireless transceiver to receive a signal through the LTE network; asoft buffer configured to store a plurality of soft channel bits for upto a maximum number of hybrid automatic retransmission request (HARQ)processes; and a signal processing unit to: determine a total number ofsoft channel bits based on the maximum number of HARQ processes, asubblock interleave size, a coding rate, and a number of code blocks,wherein for half-duplex frequency division duplexing (HD-FDD), thesignal processor determines the total number of soft channel bits basedon a reduced maximum number of HARQ processes; and store, with limitedbuffer rate matching (LBRM), a reduced number of the total number ofsoft channel bits in the soft buffer.
 12. The MTC device of claim 11,wherein the reduced number comprises half of the total number of softchannel bits.
 13. The MTC device of claim 11, wherein the soft buffer issized to store only the reduced number of the total number of softchannel bits.
 14. The MTC device of claim 11, wherein the MTC device isdefined in the LTE network within a user equipment (UE) categorycorresponding to 25344 total number of soft channel bits for downlinkcommunication with an Evolved Universal Terrestrial Radio Access Network(E-UTRAN) Node B (eNB), and wherein the reduced number of the totalnumber of soft channel bits comprises 12672 bits.
 15. The MTC device ofclaim 14, wherein the maximum number of HARQ processes is eight.
 16. TheMTC device of claim 11, wherein the reduced maximum number of HARQprocesses comprises four HARQ processes, and wherein the reduced numberof the total number of soft channel bits comprises 6336 bits.
 17. TheMTC device of claim 11, wherein the reduced maximum number of HARQprocesses comprises three HARQ processes, and wherein the reduced numberof the total number of soft channel bits comprises 4752 bits.
 18. Amachine type communication (MTC) device configured to communicatethrough a long term evolution (LTE) network, the MTC device comprising:a wireless transceiver to receive a signal through the LTE network; asoft buffer configured to store a plurality of soft channel bits for upto a maximum number of hybrid automatic retransmission request (HARQ)processes; and a signal processing unit to: determine a total number ofsoft channel bits based on the maximum number of HARQ processes, asubblock interleave size, a coding rate, and a number of code blocks,wherein the signal processor determines the total number of soft channelbits based on a reduced maximum number of HARQ processes, and whereinthe reduced maximum number of HARQ processes is based on a HARQ roundtrip timer (RTT); and store, with limited buffer rate matching (LBRM), areduced number of the total number of soft channel bits in the softbuffer.
 19. The MTC device of claim 18, wherein the reduced numbercomprises half of the total number of soft channel bits.
 20. The MTCdevice of claim 18, wherein the soft buffer is sized to store only thereduced number of the total number of soft channel bits.
 21. The MTCdevice of claim 18, wherein the MTC device is defined in the LTE networkwithin a user equipment (UE) category corresponding to 25344 totalnumber of soft channel bits for downlink communication with an EvolvedUniversal Terrestrial Radio Access Network (E-UTRAN) Node B (eNB), andwherein the reduced number of the total number of soft channel bitscomprises 12672 bits.